The present invention relates in general to flow measuring devices and methods, and in particular, to a new and useful technique for measuring the flow rate of a moving packed bed of solid particles.
One possible approach for measuring the low-velocity flow of a packed bed of particles is to weigh the material from the bed flowing from a tap for a particular period of time. Another approach is to insert some sort of mechanical flow meter into the bed itself. If the bed is at high temperature, however, neither of these approaches is practical. Measuring the rate of flow, at low velocity, for example, of a bed of sand or crushed limestone flowing downward, in a standpipe, in which the bed temperature is high (e.g., 1,600.degree. F.), poses particular problems. The bed is not fluidized and thus, is essentially incompressible.
U.S. Pat. No. 3,739,636, to Versaci et al discloses a flow meter for determining the flow rate of a fluid through a conduit wherein a signal having a magnitude that is inversely proportional to the time elapsed for a substance carried by the fluid to travel a fixed distance is produced and converted into a flow rate indication.
U.S. Pat. No. 4,170,311, to Spaw discloses a level measuring system which measures a variable level within a sensing area containing a mass of material. A sensing probe is positioned within the area and is coupled to a tank of an oscillating circuit through a switching network. A reference probe positioned in or near the sensing area is also coupled through the switching network to the tank of the oscillating circuit. The frequency of oscillation depends upon a physical parameter of the mass material within the immediate vicinity of the sensing probe. A signal processing mechanism is coupled to the oscillator for processing this frequency change. The sensing probe can be a cable antenna extending vertically into a material container for measuring the level of material therein.
Neither reference solves the problems posed above with regard to measuring low velocity flow of a packed bed of particles.